This invention relates in general to magnetic storage devices in which information is recorded on a plurality of tracks. More particularly, this invention relates to a magnetic tape recorder in which information is recorded on a plurality of spaced longitudinal magnetic tracks running parallel to the direction of movement of the tape and in which a pair of magnetic heads are positioned for optimally reading information from a pair of magnetic tracks.
In magnetic storage devices, such as magnetic disc drives and magnetic tape recorders, information is recorded on a plurality of magnetic tracks which are written and read by means of one or more magnetic heads. The head(s) is laterally movable across the width of the tracks to access a specific track or tracks for reading or writing information. In such devices, difficulties are encountered in positioning a magnetic head relative to a recorded track in order to produce an optimal output signal. For example, in a magnetic tape recorder in which information is recorded on a plurality of longitudinal tracks on magnetic tape, variability of tape position due to tape slitting tolerances, guide tolerances, etc., makes it difficult to determine the exact position of a recorded track with sufficient accuracy to insure correct reading of the data. In order to obviate such difficulties it has been proposed to sense the edge of the tape by means of optical or magnetic sensors. This technique however, does not insure that the reading head will be positioned optimally over a recorded track, since the recording head may be mispositioned due to variation in manufacturing tolerances in the positioning mechanism, due to inaccurate tape tracking and due to errors in the relative location of a write/read head. Such positioning errors are exacerbated in magnetic tape recorders in which a pair of spaced magnetic heads read information simultaneously from a pair of spaced magnetic tracks on the tape.
Various techniques have been proposed for properly positioning a magnetic head with respect to a previously recorded magnetic track in magnetic disc devices. Thus, for example. U.S. Pat. No. 4,485,418, dated Nov. 27, 1984, entitled SYSTEM AND METHOD OF LOCATING THE CENTER OF A TRACK ON A MAGNETIC STORAGE DISC, inventor Robert A. Bremmer, discloses a system and method of positioning a magnetic transducer over the center of a previously recorded magnetic track on a rotating magnetic storage disc. As disclosed, the amplitude of a feedback signal from a magnetic transducer, as it is moved in increments across a recorded track, is measured and compared to a predetermined reference level. An offset measuring system connected to a computer measures the number of increments during which the feedback signal exceeds the reference level; a calculation is made to determine the center position of the magnetic track; and the transducer is moved to this position. There is no disclosure in this patent of any means for simultaneously positioning a pair of spaced magnetic heads relative to a pair of magnetic tracks, in order to produce optimal signals from both tracks. U.S. Pat. No. 4,575,775, dated Mar. 11, 1986; entitled MAGNETIC RECORDING DISC HAVING A SECTOR SERVO PATTERN FOR USE WITH A MULTIPLE ELEMENT HEAD; inventor David W. Albrecht, discloses a device including a magnetic disc containing prerecorded servo signals for use with a multiple element head. The pattern of servo signals are circumferentially alternated in radially spaced concentric tracks so that only one head, of a pair of magnetic heads, senses servo signals for data track following by both magnetic heads. The system disclosed in this patent is disadvantageous in requiring the use of prerecorded servo signals and in failing to provide optimization of positioning of both magnetic heads simultaneously relative to associated data tracks.